1. Field of the Invention
The present invention relates to a cryogenic refrigerator including a refrigerant tube comprising two tubes that are arranged on a cooling stage substantially parallel to each other and are in communication with each other through a gas passage formed in the cooling stage. More particularly, the present invention relates to a cryogenic refrigerator suitable for a regenerative type cryogenic refrigerator such as a GM (Gifford-McMahon) type and a pulse tube type, which can effectively reduce vibration of a cooling stage due to oscillating gas pressure and can reduce the size of the cryogenic refrigerator.
2. Description of the Related Art
As a small-sized cryogenic refrigerator applied to a medical MRI diagnostic machine, a cryopump, and the like, a GM cryogenic refrigerator shown in FIG. 1 and a pulse tube cryogenic refrigerator shown in FIG. 2 have been conventionally known widely (see Japanese Patent Laid-Open Publication No. 2002-106993 (Patent Document 1), for example).
The GM cryogenic refrigerator 100 shown in FIG. 1 includes a refrigerant tube 110 comprising a regenerator 106 and a cylinder 108 that are arranged on a cooling stage 102 substantially parallel to each other and are in communication with each other through a gas passage 104. The cylinder 108 accommodates a displacer 112 therein, which is driven by a motor 114 to reciprocate in the cylinder 108. This GM cryogenic refrigerator 100 supplies high-pressure gas to the refrigerant tube 110 and collects low-pressure gas from the refrigerant tube 110, by means of a compressor 116 and the displacer 112, thereby generating cold in the cooling stage 102.
On the other hand, the pulse tube refrigerator 120 shown in FIG. 2 includes a refrigerant tube 130 comprising a regenerator 126 and a pulse tube 128 that are arranged on a cooling stage 122 substantially parallel to each other and are in communication with each other through a gas passage 124. This pulse tube cryogenic refrigerator 120 supplies high-pressure gas to the refrigerant tube 130 and collects low-pressure gas from the refrigerant tube 130 by a compressor 132, thereby generating cold in the cooling stage 122.
However, the GM cryogenic refrigerator 100 and the pulse tube cryogenic refrigerator 120 that are conventionally known has a problem that pressure oscillation of the gas in the refrigerant tube 110, 130 causes elastic extension and contraction of the refrigerant tube 110, 130, which causes the cooling stage 102, 122 to vibrate. In addition, according to the pulse tube cryogenic refrigerator 120, vibration can be reduced as a whole because it includes no portion mechanically driven, such as the displacer 112 in the GM cryogenic refrigerator 100. However, the pulse tube cryogenic refrigerator 120 is not much different from the GM cryogenic refrigerator 100 in terms of the aforementioned vibration of the cooling stage caused by elastic extension and contraction of the refrigerant tube.
As a solution of the above problem, Publication of Japanese Patent No. 2995144 (Patent Document 2) has proposed a refrigerator including two displacers that are driven in phase or in reversed phase so as to reduce vibration.
This conventionally known refrigerator has a certain effect on reduction of vibration by inertial force because vibration reduction is achieved by forming the cylinder, a connecting member of a cooling portion, and a supporting member to have polygonal shapes so as to increase the mechanical strength. However, there is a limit to reduction of vibration caused by elastic extension and contraction of the refrigerant tube in this refrigerator.